1. Field of the Invention
The present invention relates to an inkjet ink, a method for producing the inkjet ink, an ink cartridge, and an inkjet recording method.
2. Description of the Related Art
An inkjet recording method is a recording method for forming an image by applying ink droplets onto a recording medium, such as plain paper or a glossy medium. As the price is reduced and the recording speed is increased, this method is rapidly spreading. In addition, as digital cameras are spreading rapidly, and the quality of images formed by the inkjet recording method becomes enhanced, it is increasingly demanded that the inkjet recording method produce recorded matter that is substantially equal in quality to silver halide photographs.
In order that the recorded matter produced by the inkjet recording method is substantially equal in quality to silver halide photographs, images formed by the inkjet method may be required to have properties including relatively high color developability and fastness. When recorded matter produced with a yellow ink is stored in a high-humidity atmosphere for a long time, the coloring material of the recorded matter may easily migrate, which may change the color tone of the image or fade the image; hence such recorded matter may be inferior in moisture-fastness. In particular, images formed with yellow inks tend to be inferior in moisture-fastness to those formed with cyan inks or magenta inks. Accordingly, studies have been conducted on the moisture-fastness of images formed with yellow inks.
In order to enhance the moisture-fastness of images, Japanese Patent Laid-Open Nos. 02-233781 and 04-233975 propose inks containing coloring materials having a specific structure, including C. I. Direct Yellow 86 or C. I. Direct Yellow 173. Japanese Patent Laid-Open No. 2004-285269 proposes that use of a novel additive enhances the moisture-fastness of images.
In addition, recorded matter produced by the inkjet recording method tends to have lower gas-fastness and light-fastness than silver halide photographs. More specifically, the coloring material of recorded matter may be degraded by being exposed to light, humidity, heat, ozone gas or the like in the air for a long time. Consequently, the image is liable to deteriorate in color tone or fade.
Proposals have been made to enhance the gas-fastness and light-fastness of images formed with yellow inks. Japanese Patent Laid-Open Nos. 11-70729 and 2001-288391 propose yellow dye inks that can produce images having high color developability, ozone-fastness, and light-fastness. These yellow dye inks contain C. I. Direct Yellow 132 as a yellow dye.
As described above, various studies have been made to enhance the fastness properties of images formed with yellow inks. However, no approach has yet achieved a yellow ink that adequately satisfies recent requirements for high-level color developability, moisture-fastness, gas-fastness, and light-fastness.